Many systems for obtaining a positive color image by diffusion transfer processes have been proposed.
For example, U.S. Pat. Nos. 4,559,290, 4,356,249 and 4,358,525, JP-A-53-35533 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-53-110827, JP-A-54-130927, JP-A-56-164342, JP-A-59-154445 and JP-A-62-215270 disclose methods wherein a dye providing compound of an oxidation type incapable of releasing a dye, is allowed to coexist with a reducing agent or a precursor thereof. The reducing agent, being present in an amount corresponding to the exposure amount of silver halide, is oxidized by wet development or heat development and the compound is reduced by the reducing agent left behind, without being oxidized to release a diffusing dye. EP-A-220746 and Japanese Published Technical Report (Kokai Giho) 87-6199 (Vol. 12, No. 22) disclose color light-sensitive materials using a non-diffusing compound capable of releasing a diffusing dye by the reductive cleavage of an N-X bond (wherein X is an oxygen atom, a nitrogen atom or a sulfur atom), as the compound capable of releasing a diffusing dye by a similar mechanism to that described above.
However, it has been found that there is a problem in that dye images are highly stained when the aforesaid reducible dye providing compound together with a reducing agent or a precursor are used in combination with a silver halide emulsion.
The use of a diffusing electron transfer agent in addition to a non-diffusing electron donor as a reducing agent is effective in inhibiting the staining of the positive image-forming light-sensitive material using the aforesaid reducible dye providing compound. However, the oxidant of the electron transfer agent formed by development diffuses into other layer having different color sensitivities where the electron donor is oxidized. Thus, the density of the image is lowered and color reproducibility is deteriorated. An attempt has been made to reduce the oxidant of the electron transfer agent so diffused by providing an interlayer between light-sensitive layers having different color sensitivities from each other and containing a reducing agent in the interlayer.
However, in a diffusion transfer type light-sensitive material, there is a limitation on the amounts of a binder and a reducing agent which can be added to each layer from the viewpoints of image-forming rate, resolving degree, layer quality, etc. Accordingly, it has been desired to make further improvements in this regard.
For example, reducing agents described in U.S. Pat. No. 4,277,553, JP-A-61-75344 and JP-A-61-75348 are lacking in the ability of reducing the oxidant of the electron transfer agent diffused and can not sufficiently inhibit lowering in the density of the image in unexposed area.
Reducing agents described in U.S. Pat. Nos. 4,198,239 and 4,732,845, EP-A-351860, EP-A-284082 and EP-A-357040 and JP-A-63-198052 and JP-A-1-154151 can effectively reduce the oxidant of the electron transfer agent diffusing into the interlayer to thereby inhibit lowering in the density of the image in the unexposed area. However, such reducing agents themselves have strong reducing power, and hence a small amount of the reducing agent diffused reduces the reducible dye providing compound, and color turbidity is caused.
Accordingly, it is desirable that the reducing agent contained in an interlayer of a diffusion transfer type light-sensitive material has such characteristics that the agent has the ability to effectively reduce the oxidant of the electron transfer agent and the agent itself does not have an adverse influence on other layers and photographic characteristics as described above.